Field of the Invention
The present invention relates to an image capturing apparatus and a method for controlling the image capturing apparatus, an image stabilization apparatus and a method for controlling the image stabilization apparatus, and lens unit.
Description of the Related Art
Conventionally, image capturing apparatuses capable of panning shooting are known. Panning shooting refers to a technique of shooting, in a case where a subject is moving at a certain speed, an image in which the background flows while the subject appears to not be moving, by exposing the image while panning an image capturing apparatus so as to follow the movement of the subject. In panning shooting, usually, shooting is performed at a slow shutter speed so as to express a sense of dynamicity in the subject.
However, skill is required to follow a subject (e.g. a train that is moving at 60 km/h) well while panning the camera at a slow shutter speed (e.g. 1/30 seconds) to shoot the subject. In particular, for beginners, it is difficult to adjust the camera panning speed to the subject speed during an exposure period at a slow shutter speed, which is why panning shooting is a difficult shooting technique. To enable such panning shooting to be readily performed, a method using an image stabilization apparatus is known.
In general, a good example of a pan shot is an image in which a subject stands still while the background flows in a direction opposite to the moving direction of the subject. To shoot such an image in which a subject stands still, Japanese Patent Laid-Open No. 2006-317848 discloses a method in which the difference between the subject speed and the camera panning speed is detected, and correction is performed according to the shift amount corresponding to this difference, using an image stabilization function. With this method, immediately before shooting, the angular velocity of the camera that is following the subject during the panning (or tilting) is detected by an angular velocity sensor in the camera. Simultaneously, the moving amount of a main subject image on an imaging plane is detected. The angular velocity of the subject is calculated from the detected panning speed and moving amount of the subject image on the imaging plane. During exposure, an image stabilization operation is performed in accordance with the amount of difference between the calculated angular velocity of the main subject and the output from the angular velocity sensor in the camera. Thus, the vibration amount and the difference between the speed of the main subject and the camera panning speed are corrected, which enables suppression of image blur of the main subject subjected to panning shooting.
Japanese Patent Laid-Open No. 2015-161730 discloses an image stabilization apparatus that causes timing of the output of the moving amount of a subject image on an imaging plane and the output from a vibration detection unit to coincide with each other, and improves the accuracy of detection of the angular velocity of the subject. Japanese Patent Laid-Open No. 2015-102774 discloses a photographic apparatus that determines a shutter speed to be used when capturing an image of subject light with an image sensor based on an angular velocity and a focal length.
It is, however, difficult for a beginner to set a correct shutter speed for shooting an image in which the background flows by an appropriate amount in a direction opposite to the moving direction of the subject. This can be comprehended from experience because the shutter speed is determined based on the subject speed, the focal length of the imaging lens, the shooting distance from the subject, and the panning (or tilting) speed of the photographer.
If the shutter speed is too fast, the subject is less likely to blur but the background does not flow, resulting in the subject appearing less dynamic, and an obtained image may not be satisfactory when considered as an exemplary work of panning shooting. On the other hand, if the shutter speed is too slow, the background flows but the exposure period becomes long, thus the subject is likely to blur due to a camera shake, which results in an increase in the likelihood of failing the panning shooting.
In addition, Japanese Patent Laid-Open No. 2015-161730 does not disclose an assist function for setting an exposure period when panning shooting is performed. For this reason, it is difficult for a photographer who is not used to panning shooting to calculate an appropriate exposure period to obtain an intended flow amount. In the image capturing apparatus disclosed in Japanese Patent Laid-Open No. 2015-102774, consideration is not given to variation in speed in the same subject. For example, when shooting a running animal, a part of the subject may flow in the obtained image depending on the settings. This phenomenon occurs when a fast-moving portion exists in the subject and a long exposure period is set relative to the moving speed of this portion, and the image shot at this time may lose its ambience brought out by panning shooting.